The invention relates to a power supply device, particularly suitable for supplying power to a filament of a transmitter tube, provided with a filament transformer, a pulse transformer and terminals for an AC generator, where a secondary side of the filament transformer is coupled with the filament, a primary side of the filament transformer is coupled with the terminals and where a secondary side of the pulse transformer is coupled with the filament.
Such a device can be applied in a radar transmitter for the generation of radar transmit pulses. The radar transmitter will be provided with a high-power radar transmitter tube, such as a cross-field amplifier, a travelling wave tube or a klystron, whose cathode is at a pulsed high-voltage potential. A problem, however, is posed by the filament, which forms the cathode or is contained in the cathode and which must be supplied with a filament voltage. Filament voltage is required to heat the cathode to a high temperature, to ensure electron emission to a sufficient degree.
On the basis of a solution, known from the literature, it is essential to the filament voltage transformer that the capacitance between the primary and secondary winding is very small, since this capacitance forms a parasitic load on the pulse transformer which supplies the cathode of the radar transmitter tube with pulsed high voltage. This type of transformer having a small capacitance between the windings is known to possess a high leakage self-inductance, as a result of which, in loaded condition, the output voltage among other things depends on the frequency of the primary voltage and the temperature of the transformer. As such this transformer is less suitable for supplying a filament, whose voltage has been stipulated by the manufacturer.